Spark plug



May 15, 1951 o. E. BowLus ET AL 2,984,760

SPARK PLUG Filed Nov. 15, 1957 INV RIS l ,Baza s. 7777655; /7 Gra .4777

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United States Patent hice SPARK PLUG Omer E. Bowlus, Detroit, and Kenneth A. Graham, Birmingham, Mich., assignors to Chrysler Corporation, Highland Park, Mich., a corporation of Delaware Filed Nov. 15, 1957, Ser. No. 696,845 1 Claim. (Cl. 313-141) The present invention relates to internal combustion engines tand has particular reference to an improved spark plug therefor.

A principal object of the present invention is to provide a new and novel design for a spark plug.

Another object of the invention is to provide a novel spark plug construction which accommodates a selfcleaning action during operation.

A further object is to provide a novel spark plug which is not susceptible to spark plug heat-up which eifects many spark plugs now in use.

Still a further object of the invention is to provide a new and improved spark plug which is easily and economically manufactured.

More particularly, the invention relates to a new and improved type of surface-gap spark plug. The tiring end of the plug is provided with two nested frusto-conical molybdenum washers which provide a circular gap for for the spark to bridge. One washer is pressed against the outer shell of the plug while the other is pressed against the center electrode.

Other objects and advantages will become more apparent from the following description of the embodiments of our invention, reference being had to the accompanying drawings in which:

1Fig. l is a longitudinal sectional view of the spark p ug.

Fig. 2 is a partial view in section of the lower end of the plug shown in Fig. l, wherein the tiring end of the plug has been ground down to provide a predetermined spark gap size.

Fig. 3 is an end view taken in the direction of the arrow 3 shown in Fig. 2.

Fig. 4 is a transverse sectional view taken on the line 4 4 of Fig. 1.

Fig. 5 is a transverse sectional view taken on the line 5-5 of Fig. l.

Referring to the drawings, there is shown a spark plug generally indicated by the numeral comprising an outer shell 12 of generally cylindrical configuration which has a reduced section 14 integrally connected to a relatively larger section 16. The shell 12 is provided with a bore 18 which terminates adjacent the end of the small section 14 at one end and communicated at its other end with a larger internally threaded bore 20. The small section 14 is provided with external threads 22 which are used to secure the plug to the engine block and at its lower end is provided with an internal annular shoulder 24 having a frusto-conical surface 26.

A center electrode 28 has its lower portion extending concentrically through the shell 12. The lower end of the electrode 28 terminates adjacent the lower` end of the small section 14 of the shell and is provided with an enlarged radially outwardly extending portion 30 having a frusto-conical surface 32. At the upper end of the shell and above the shell the electrode 28 is spaced from the shell by a substantially cylindrical insulator 34. The lower end of the electrode 30 is spaced from the internal 2,984,760 Patented May 16, 1961 side walls of the small section 14 of the shell by another insulator 36 of donut-like conguration. The insulators 34 and 36 are preferably made of porcelain, but other types of material known in the art could be used. To accommodate a concentric spark gap in the improved plug, there are provided frusto-conical washers 38 and 40. The washers 38 and 40 are disposed at the bottom of the plug and are in a coaxial nested relationship wherein the base diameter of the washer 40 is smaller than the diameter of the constricted end of the washer 38 to thereby form a small gap therebetween. The washers 38 and 40 may be made of any suitable metal or alloy. In actual construction it has been found that the use of molybdenum washers is very satisfactory. The coniiguration of the lower end of the insulator 36 is predetermined so that it engages both washers 38 and 40 and urges the washer 38 against the frusto-conical surface 26 of the shoulder 24 on the shell and also urges the washer 40 against the frusto-conical surface 32 on the enlarged end 30 of the electrode 28. By this construction the washers 38 and 40 are held in a iixed position, as clearly shown in Fig. l. A collar 42 clampingly engages the electrode 28 and holds the insulator 36 in position. The collar 42 may be press tit on the electrode 28 but is preferably spot welded or silver soldered thereto.

To complete the construction of the plug 10, the upper portion of the `bore 18 is filled with a packing come pound 44, thereby forming a gas seal. The packing compound may be any suitable granulated substance. In actual construction, a mixture of talcum powder and aluminum oxide was found to be very satisfactory. The packing compound 44 is iirst compressed and then maintained in a compressed condition by the insulator 34, the bottom surface of which engages the packing compound. The insulator 34 is provided with an annular shoulder 46, which receives a washer 48 on the top thereof. A jamb nut 50 is threaded into the internally threaded bore 20 of the large section 16 of the shell and engages the washer 48 to thereby urge the insulator 34 downwardly against the packing material 44.

The upper end of the electrode 28 is threaded to re ceive a metal cap 52 which is turned down on the electrode to a tightened condition with a washer `54 disposed between cap 52 and the upper surface of the insulator 34.

In viewing Fig. l at the lower portion thereof, there will be seen a reference line 56. The reference line 56 represents the location at which the most eicient spark can be obtained. As a result, after the spark plug is assembled, it is ground down to the reference line 56. Fig. 2 illustrates the lower end of the plug after it has been ground down. It will be noted that the dielectric between the` washers 38 and 40 is the lower circular tip of the insulator 36 and that, therefore, there is no air between the closest adjacent points or surfaces of the washers 38 and 40. In View of the fact that the dielectric 4constant of the insulators 34 and 36 is higher than that of air, the voltage required to cause a spark between the washers 38 and 40 will be lower than that required to bridge an air gap. As a result, the spark plug 10 is of the type known as a low voltage spark plug. It will also be noted that there are no protruding elements at the spark gap which will become heated during the operation of the plug. As a result the plug remains relatively cool during operation and no pre-ignition will be caused. By utilizing the construction shown herein, the spark plug will be ia self-cleaning spark plug. If any .deposits are formed on the insulator between the washers 38 or 40, the next spark will come at the location where the deposit is formed and will thereby burn the deposit oif causing the aforementioned self-cleaning action.

While we have illustrated and `described several embodiments of our invention, it is to be understood that such is yfor the purpose of illustration only, and it is contemplated that those skiled in the art may modify certain ydetails without departing from the spirit or scope of the invention as defined in the claim appended hereto.

We claim:

A spark plug comprising an outer metallic shell, a centnally disposed elongated electrode extending through said shell and having one end thereof terminating adjacent one end of said shell, said one end of said electrode being ared outwardly to form a frusto-conical seat, said one end of said shell being flared inwardly to form a frustoconical seat spaced from the flared end of said electrode, inner and outer coaxally disposed frusto-conical washers disposed around said terminal end of said electrode, the outer surface of said outer washer being parallel to and engaging'said seat on said shell and the inner surface of said inner washer being parallel to and engaging said seat on said electrode, the base of said inner washer being smaller in diameter than the constricted end of said outer washer and disposed adjacent thereto to form a spark gap therebetween, insulating means disposed between said eletcrode and said shell and wedgingly engaging said washers, and means urging said insulating means into said wedging engagement.

References Cited in the tile of this patent UNITED STATES PATENTS 2,088,945 Xardell Aug. 3, 1937 2,255,203 Wiegand Sept. 9, 1941 2,391,456 Hensel Dec. 25, 1945 2,527,489 Smits Oct. 24, 1950 2,578,754 Smits Dec. 18, 1951 2,684,665 Tognola July 27, 1954 2,699,158 Purdy et al. Jan. 11, 1955 FOREIGN PATENTS 22,517 Great Britain Sept. 28, 1910 

